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U.S. customary and metric units

Learn to sort units of measure into two categories: U.S. Customary and Metric units. Created by Sal Khan and Monterey Institute for Technology and Education.

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  • leafers seed style avatar for user Laura
    What is 1/1000 of a litre? kilolitre or millilitre?

    Also, can centi be used in all 3 units of measurement i.e. centilitre, centrigram as well as centimeter?

    Lastly, same question for deci. Can it be used for decilitre and decimeter as well as decigram?
    (62 votes)
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  • spunky sam blue style avatar for user Samir Gunic
    The (British) imperial system or the "US customary" system currently used in the US is so outdated. United States is one of three countries in the world that still uses these messy English units, alongside Myanmar and Liberia. It's the measurement system of the old world - these English units date back at least to the middle ages! Even the Brits have gone metric!

    So what's stopping the US from adopting the International System of Units or the "metric system" as its official and primary system of measurement? Is it the cost of the transition? Or is it the American urgent need for "individuality"?

    The metric system is 10 times better!
    (14 votes)
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    • duskpin ultimate style avatar for user The5thStrongBadianAmendment
      I'll posit that Americans are, generally speaking, happy with the imperial system. They don't want to learn the new system, because this one works fine for them. Also, road signs and gas stations currently use miles. While retrofitting gas stations to use metric probably would be cheap (though there isn't much demand for them to do so), changing old road signs from using miles to kilometers would be very expensive and would require a complete revamp of our road systems.
      (9 votes)
  • leaf red style avatar for user nathan.birks
    Why is metric better?
    (9 votes)
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    • mr pink red style avatar for user Shihab M.
      Metric has more value and responsibilities. It is common around the world. It is the main system to measure. It used in India,Germany.Russia,Netherlands and many more sights in the world. Our Us Customary System has less responsibilities cause of the metric system
      (9 votes)
  • leaf grey style avatar for user Will D.
    How did the U.S. get this separate system of measurement in the first place?
    And why did the U.S. government decide not use the metric system or SI units?
    (10 votes)
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  • hopper cool style avatar for user Ralph Gifford 5
    At -, Sal mentions that there are two measurements called "ounces." how did something like this happen? I know that in the metric system, the units of mass, volume, and distance are connected, for one cubic centimeter = one milliliter, and the gram was originally calculated as the mass of one milliliter of water. However, I want to know if there is any connection between fluid ounces (for volume) and ounces (for weight).
    (5 votes)
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    • duskpin ultimate style avatar for user Polina Vitić
      Historically, a fluid ounce was equal to the volume of one ounce of a liquid (water, beer, wine, etc.) - but this meant that the actual volume of 1 fluid ounce would differ from one substance to another.

      At present, 1 oz of pure water is roughly equal to 1 fl oz of pure water. If you measure 1 fl oz of other liquids, however, they may or may not weigh 1 oz.

      Hope this helps!
      (3 votes)
  • blobby green style avatar for user bmcgee318
    why is it that the United States does not use the metric system?
    (2 votes)
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    • hopper cool style avatar for user Chuck Towle
      In the United States, students have been learning both systems for at least 40 years. And both systems are pretty widely understood and used in the U.S.

      Becasue the US Government has limited power to demand that everyone use only the decimal system, both systems have continued to be used because that it what people choose to do.
      (9 votes)
  • leaf red style avatar for user NCM
    Why is the US customary system based on ambiguous numbers like 3, 12, and 1280?
    (4 votes)
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    • leafers ultimate style avatar for user Alan Tennant
      There not ambiguous, but the customary measurements are all sorts of orquard and outdated.

      However a small benifit is that a high proportion of natural numbers smaller than numbers like 12 and 360 are factors of those numbers, unlike 10 and 1000.

      10: 2, 5
      12: 2, 3, 4, 6
      1000: 16 factors, lowest few being: 2, 4, 5, 8, 10
      360: 24 factors, including 2, 3, 4, 5, 6, 7, 8, 9, 10
      (0 votes)
  • aqualine ultimate style avatar for user maverickjayden
    how is a decameter some times always one i though it was some 2
    (3 votes)
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  • piceratops ultimate style avatar for user Wilbur Donovan
    Can someone tell me why the U.S prefers different units?
    (2 votes)
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  • aqualine ultimate style avatar for user Kaleab Paddock
    why do we use kilograms if we have u.s cusdtory ?
    (1 vote)
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Video transcript

We're asked to sort the following units of measurement into two categories: U.S. customary units and metric units. So these are just two different systems. You'll get more and more familiar with them. Then indicate whether each unit measures length, weight, mass, or volume. Let's do the first. Let's see which of these are U.S. customary unit versus metric units. So the liter is a metric unit. You would use it in the metric system. A gallon is a U.S. customary unit. We've been dealing with that. If you fill your gasoline in Europe, you're going to be filling it in terms of liters. In the U.S., you're going to be filling it in terms of gallons. And we're going to talk about whether they're units of volume and whatnot in a little bit. Decigram, that is metric system. In general, whenever you see these prefixes, deci, centi, kilo, you're dealing with the metric system. No one ever talks about a kilopound. I guess you could, but no one really talks about it. Same thing, millimeter. This is metric system. A gram is metric system. Meter is metric system. The foot is a U.S. customary unit. We'll talk about whether it's distance or any of that in a little bit. Kilogram, once again, it is metric units. In case you haven't gotten what I'm doing here, blue for metric, red for U.S. customary units, or I guess magenta. Centiliter, that is metric. Centimeter, meters are metric. And notice we have the prefix in both cases. Centi means 1/100. Cup, that is U.S. customary units. I have to do that in the magenta. Cup, U.S. customary units. Meter, that is the metric system. Pound, U.S. customary units. It's getting a little tedious. Inch, same thing, that's what we use in the U.S. Ounce, we use that in the U.S. And then the yard, we also use that in the U.S. Now we've divided them up. All the magenta ones are used in the U.S. All of the blue ones are used really in the rest of the world, and actually some places in the U.S. as well. I think a lot of the world is frustrated that the U.S., that we're not all converted to this because the metric system is actually a little bit more logical. It's easy to just figure out what it's saying, and we'll deal with that in more detail in the future. Now the next thing we to figure out is whether something is a measure of length, weight/mass-- and they're not exactly the same thing. Mass is how much of a substance you have. Weight is how much force with which gravity is pulling on that mass. And it would change depending on what planet you're on. But on Earth, they tend to be used interchangeably, so we'll use it roughly interchangeably here. And then you have volume, or how much space something takes up. So this is distance. This is moving in one dimension. Mass is how much stuff there is. Weight is how much the force that stuff is pulled on, on a planet, by gravity, or I guess a star anywhere. And volume is how much space does that stuff take up. Now let's think about it. Liter is volume. This right here is volume. How much space do you take up. Gallon is also volume. That's in the U.S. And in Europe, or in the metric system, it would be a liter. That's a gram. Gram is a unit of mass. So decigram just means 1/10 of a gram. Millimeter. Meter is a unit. Meter right here, that is the unit of distance or of length. Millimeter, milli means 1/1,000 of a meter. Foot, that is also a unit of length. Kilogram, that just means 1,000 grams. Kilo means a thousand. Gram, we already said, is a unit of mass. Centiliter, that means 1/100 of a liter. Liter, we already figured out, is a unit of volume. Centimeter, we already figured out. Meter is a unit of length. Centimeter means 1/100 of a meter. So this is a unit of length. Cup, we've seen multiple times already. It is a unit of volume, how much space does something take up. Meter, that is length. We've seen it multiple times already. Pound, that is actually a unit of weight. An inch is a unit of length. We're all familiar with it. An ounce-- you have to be careful here-- if someone just has an ounce, that is 1/16 of a pound. It as a unit of weight. If it was written fluid ounce, then we'd be talking about 1/16 of a pint, and then it would be a unit of volume. But since it's just ounce, it's a unit of weight, 1/16 of a pound. And then finally, a yard is a unit of length. And we are done.